Abstract: To investigate the buckling failure mechanisms of stiffened cylindrical shells under multiple deep-water explosion loads, this study employs the acoustic-structure coupling method with finite element analysis. The explosion load curves were constructed based on the Geers-Hunter semi-empirical formula, with load controlled by the explosive shock factor. And numerical simulations were conducted under 400 m water depth and stand-off distances of 0.5-1.0 m to analyze the effects of load characteristics and structural parameters on buckling failure. The results show that: the typical buckling failure process of internally stiffened cylindrical shell structures under deep-water explosion can be divided into: initial deformation stage, local instability stage, instability intensification stage, and final failure stage. The primary cause of buckling failure is attributed to the cumulative damage deformation of the structure reaching the critical instability threshold under corresponding hydrostatic pressure conditions. Shockwave loading induces initial deformation defects, while bubble pulsation pressure dominates buckling failure of the structure. Standoff distance significantly affects the structural bucking failure modes. When the standoff distance is 0.5-0.7 m, the structure is dominated by central local bucking; when the standoff distance increases to 0.8-1.0 m, the failure mode shifts to end-dominated local bucking. Due to the limitation of structural damage area, the critical buckling deformation of the end-dominated mode is significantly larger than that of the former. And the critical buckling deformations under both modes exhibit an exponential decay trend with the increase of standoff distance. The reduction in the moment of inertia of internal stiffeners weakens the bearing capacity and explosion resistance performance of the structure, leading to the expansion of the instability region from the front face to the circumferential direction. Moreover, the decrease in overall stiffness significantly increases the critical buckling deformation of the structure. These findings provide fundamental support and insights into the safety design of cylindrical shell structures against deep water explosion.